Steering device



y Q, A. v. BEDFORD 2 STEERING DEVICE Filed Nov. 6, 1940 3 Sheets-Sheet l PROJECTOR POSITIONS .15 71 3nventor fllda V Bedford 0 9; and. an s. -j}

July 30, 194%. v BEDFQRD 2,494,942

STEERING DEVICE Filed Nov. 6, 1940 3 Sheets-Sheet 2 3nventor Hlda VBedfod v E ttorneg Patented July 30, 1946 2,404,942 STEERING DEVICE Aida V. Bedford, Collingswood, N. J assignor to Radio Corporation of timer-lea, a corporation of Delaware Application November 6, 1940, Serial No. 364,483

16 Claims. 1

This invention relates to direction control devices which are useful in controlling the path followed by moving objects, such as aerial bombs, and the like, and has for its principal object the provision of an improved apparatus and method of operation whereby a beam of radiant energy is used to control the path of the bomb, the operator in the airplane being required only to sight the target with a conventional optical sighting device, the system then automatically correcting the path of the falling bomb so as to insure a direct hit on the target.

Modern technique for aerial bombing depends upon releasing the bomb from the airplane when it is in such a position and moving at such a velocity with respect to the target on the ground, or on the water, that the natural trajectory of the bomb along its approximately parabolic path will cause it to strike the target. While reasonable accuracy under certain conditions is attained by present methods, the uncertainties of the wind at different altitudes and at different times makes it quite difiicult to score a direct hit on a small target from altitudes above the range of anti-aircraft guns, between 15,000 to 20,000 feet, for example. The present invention is to be used in conjunction with the present systems which should be used in accordance with existing practice or perhaps in a less refined form, the control system of the present invention being an auxiliary or vernier control for guiding the bomb after its release so as to assure accuracy.

Briefly, the present invention contemplates radiating downwardly from a special projector in the airplane a beam of energy a cross-section of which is represented by four quadrants of a circle, each quadrant being differently characterized by a distinct modulation. The beam projector is geared to the optical sighting device, which may be the conventional bomb sight, and is provlded with means for automatically varying the angle between the beam and the line of sight between the airplane and the target as determined by the sighting device. The control mechanism is such that the projected beam always includes the bomb in its downward flight.

The bomb is provided with suitable fins which cause its longitudinal axis to line up with its path of fall and a gyroscopic compass which prevents rotation about that axis. A receiver for the radiant energy and a control mechanism are mounted within the bomb to operate the steering fins in accordance with the modulation frequency of the quadrant of the beam in which the bomb is at any instant, so as to return the bomb to the center of the beam. By reducing the angle between the radiated beam and the line of sight to zero in the time required for the bomb to fall from the airplane to the target, it will be appreciated that the bomb will be controlled throughout its entire flight and will be directed to the target.

This invention will be better understood from the following description when considered in connection with the accompanying drawings in which Figure 1 is a view illustrating the general operation of this invention; Figures 2 and 3 are cross-sectional views showing the modulation of the controlling beam; Figure 4 is a view partly in section of an aerial bomb; Figures 5 and 6 are sectional views of a beam projector; Figure 7 is a schematic view of the beam angle control mechanism; Figure 8 is a circuit diagram of a receiver and mechanism for operating the control vanes of the bomb; Figure 9 is an alternative form of beam projector utilizing radio frequency energy; Figure 10 is a view of an aerial bomb equipped with an antenna; Figure 11 is a receiver for controlling the bomb by means of a radio beam; and Figure 12 shows enlarged views of the imaging apertures and modulating holes in the four quadrants of the beam projector.

Principle of operation The general principle of operation of the present invention will first be described in connection with a control beam of visible light, although it is to be understood that other forms of radiant energy may be employed such as the invisible or infra-red rays, radio, and the like.

Referring to Fig. 1, an airplane I3 is flying along a substantially straight course at an assumed altitude of approximately 20,000 feet and releases a bomb l5 at the time T1 to strike a target 19. Assuming, for example, that by the conventional practice the bomb is unintentionally released slightly too soon, it then normally follows the trajectory 2| and falls short of the target IS. The present control system is so designed that the bomb is deflected from its unguided path only enough to secure a hit on the target. Thus, it is possible to use easily manipulated control vanes on the bomb and a light-control apparatus. The dotted lines 231 to 235 represent the line of sight between the airplane and the target at successive time intervals T1 to T5, it being understood that, after releasing the bomb at the time T1, the pilot continues to fly a straight course and to sight the optical sighting device on the target until the bomb has hit. Due to the effect of wind resistance, the bomb falls slightly behind the airplane and at the successive intervals illustrated the angles B1 to B5 represent the angles between the lines of sight 231 to 235 and lines 241 to 2&5 drawn from the airplane to the bomb at the successive intervals, the latter lines being the directions in which the control beam is directed at any time. It will be noted that at the instant T1, when the bomb, is released, the angle B1 is the greatest, and that the angle successively decreases until at the instant T5, when the bomb strikes the target, the

angle B5 between the line of sight and the control beam is zero.

As indicated above, the bomb is controlled by a beam of radiant energy whose axis is directed downwardly from the airplane. 'In order to establish control over the flight of the bomb at the instant it is released, the beam must be directed towards the bomb, and it must also be continuously focused on the bomb throughout its entire flight. To accomplish this without having to'actually see the bomb during its flight, it is herein proposed to automatically vary the angl between the radiant beam and the line of sight throughout the known period. required for the bomb to fall from the aircraft to the target so that the beamcontinuously intersects the normal trajectory of the bomb. This angle is gradually reduced to zero and reaches alignment with the optical line of sight at or near the end. of this interval. Since the time required .for a bomb to fall from a known altitude is independent of the wind and the plane speed, it is possible to calculate in advance the rate of change of this angle so that the bomb will at all times remain within the beam even though the operator is unable to follow its actual flight.

The beam control system Although there aremany different ways of maintaining a falling object within a beam of radiant energy, a preferred embodiment utilizing a modulated light source.- is illustrated in the drawings. Figure-2 represents a 'cross section of the control beam which is seen to be divided into trated. By means of a mechanism which will be described hereinaftenthe bomb receives light modulated at the given frequency which causes the proper vane 25 to be operated so that the bomb tends to move in such a direction that it will approach the center of the beam. It may, however, come into the quadrant modulated at 100 cycles per second. This modulation frequency is then selected in the receiver and utilized to control another vane-operating motor which operates the vane 21 to move the bomb in a direction at right angles to the original direction so that it moves towards the center again. 'The bomb may move back into the l20-cycle region, but it will again be steered towardthe center of the beam. The center portion of the beam is preferably unmodulated so that, when traversing its normal course, if properly directed, it will remain in the center of the beam and its course ject to modulation frequencies of both and cycles per second, it will be appreciated that vanes 25 and 21 will both be operated in such a direction as to cause the bomb to move along a radius of the cross-section directly toward the center of the beam. In the adjacent sectors, only -a single control frequency will be received, but

it will be seen that thebomb will then also move almost directly toward the center of the beam, as. desired. Fig. 4 is a general View of the bomb i5 showing a photoelectric tube 29 mounted in its rear, the control vanes 25 are operated'from a motor M within the bomb through a worm gear mechanism 3| against-a spring bias32, which tends to return the vanes to their normal positions when the motor is not actuated. The control vanes 21 are mounted inaplane at right angles to the vanes 25 and do not appear in the sectional drawing. It is to be understod that a gyroscopic motor is also included within the bomb to prevent its rotation about its axis;

Beam' projector A projector for producing a light beam of the type illustrated in Fig. 2 is shown in Figs. 5 and 6 to which reference is now made. A simple mechanical light projector. comprises a. rotating chopper disc 33 having four groups of apertures therein, a, b, c and d, spaceduniformly around the entire circumference of four circles of different radii, although only the apertures in each quadrant are shown. The number of the apertures and the speed of rotation of the disc, as

determined by the motor 35, is chosen so as .to

produce the desired separate modulation frequencies. The motor and disc. are mounted within a cylindrical chamber 31 inthe upper portion of .which four light sources are provided,ionly two of which appear in thesectional View of Fig. 5.

Beneath the rotating chopper disc 33 four tubular channels are arranged whose cross-sections may be square, round or any desired shape. "The first channel 5| in quadrant A has a small imaging aperture 52 in its upper end which is aligned with and slightly smaller than the inner apertures a in the rotating disc so that light from the bulb 5 concentrated by the lens 41 will pass through the disc 33 and intensely illuminate thisaperture. The shape of the imaging aperture 52 is similar to a 90-degree sector of a circle having its apex filled, and is illustratedin enlarged section in Fig. 12. The point 0, located at'the center of the circle of which the aperture is a' sector, is also the optical axis of a lens 54 which images the illuminated aperture 54 at a great distance.

The second, third and fourth channels in quadrant B; C and D are constructed similarly, the imaging apertures being in corresponding quadrants, as shown in Fig. 12, and being aligned with the correspondingly marked holes '12, c andd in the chopper disc. As a result, a beam is produced which comprises essentially'fo'ur QO-degree in substantially circular cross-section, and having an unmodulated central portion about its axis. The projected image on th ground may be of the order of several hundred yards in diameter when the airplane is flying at a great altitude.

A similar channel having a similar aperture is located in the second quadrant. The third and fourth quadrants C and D are provided with similar channels likewise. This projector produces a light beam having four equal sectors modulated at different modulating frequencies as required. The light is directed in a beam of increasing cross-section so that the beam is large enough to always include the bomb in its flight when the airplane is operating at high altitudes.

Beam angle control system The apparatus for properly directing the projector is illustrated in Fig. 7. The projector 31 is mounted on a pivot 39 of a gimbal support, not shown, which allows the projector to be swung forward or backward, right or left, with respect to the direction in which the airplane is travel ing. A telescopic sight 55 is pivoted at a bearing 51 to the projector 3'! in such a way that the angle B between the sight 55 and the projector 31 is controlled by a worm rack 59 and worm gear El. A reversible motor 63 drives a lever 65 about a pivot 61 by means of a Worm 69 and sector II. A roller I3 mounted on the end of the lever drives a gear I5 through a cam 11. Gear I5 in turn drives the worm 6| by means of a gear I9 and a flexible shaft 8 I.

In operation, the angle B is first adjusted to equal the versible motor to the proper position. As clearly indicated by Fig. 1. the angle B1 is that between a vertical line and a line extending from the observer to the target. Motor 63 is a reversible motor and its direction of rotation may be controlled by a switch 60. At the instant the bomb is dropped, the switch 62, coupled to the bomb release lever, starts the motor running in such a direction that the angle B is gradually reduced to zero in a calculated time equal to that required for the bomb to drop from the airplane to the ground. At the same time, the operator maintains the sight 55 on the target at all times. The shape of the cam TI is such that the projector approaches alignment with the sight as indicated by the successive angles B1, B2, B3, etc, in Fig. 1.

For slight variations in the altitude of the airplane from the calculated altitude for which the cam was designed, it is probable that suitable changes in the motor speed and changes in the starting point on the cam will provide adequate compensation. However, for large variations, the use of a different cam surface is desirable. A plurality of such cams may be provided corresponding to different altitudes, and the proper one selected before setting the mechanism in operation.

Receiver Fig. 8 is a circuit diagram of a receiver for use within the aerial bomb for controlling its path of flight. The receiver includes the photoelectric tube 29 which is connected to the input of a high gain amplifier 85. The amplifier output is connected in series through four frequency selective relays $1, 89, QI and Q3 which respond respectively to the four modulation frequencies assumed to be 100, 140, 120 and 170 cycles per second, respectively. These frequency responsive relays actuate associated double-pole singlethrow switches 95, 97, 99 and IBI, the switches being maintained in anopen position by any suitangle 31 of Fig. 1 by running the re- '6 able bias means, closing only when a current of the corresponding frequency is applied by the amplifier 85.

Relay 95 closes the circuit between a battery I03 and a reversible motor N35 to cause the motor to rotate in a given direction. Relay 9 closes the circuit between the same battery I83 and the reversible motor I85 so as to cause the motor to rotate in the opposite direction. Relays 99 and IEH similarly connect the battery I33 with a second reversible motor I09 to cause its rotation in respective directions. Each motor is geared to a control vane for the bomb through a suitable worm gear mechanism. The motors and vanes are returned to their normal positions by bias springs I00 and'IBZ. Thus, motor I controls the orientation of the vane 25 while the motor I69 controls the orientation of the vane 21.

It will be appreciated that the bomb at any instant will normally be responsive only to a single modulation frequency, and that only one vane will be operated at any given time. If the overlapping modulation system of Fig. 3 is used, however, both motors may be operated together in the manner described above. Suitable stops may be provided for limiting the rotation of the motors, as, for example, by limiting the gear sector, or in any other convenient manner.

For obvious reasons, the use of a light beam to control the trajectory of the bomb has certain disadvantages. Such a beam is subject to interruption by smoke or clouds, and, in addition, may be observed easily by anti-aircraft batteries on the ground. To overcome this disadvantage, the principle of operation may be applied to a system utilizing a beam of radio energy in the manner illustrated in Fig. 9. In this figure, the optical bomb sight 55 is used as before. It is similarly mounted on and used in conjunction with a radio frequency beam projector l I I which includes within it, for example, an ultra high irequency radio transmitter H3, and a parabolic reflector H5. Modulation in the four quadrants may be accomplished in the manner described in a patent issued on June 1, 1937, to Irving Wolfi, No. 2,682,042. Briefly, this is done by means of four gas modulator elements which are connected to four sources of modulation frequency, I II, I I9, HI and I23. The resultant radio frequency beam then corresponds to the light beam produced by the light beam projector illustrated in Figs. 5 and 6 and is operated in a similar manner.

In order to receive the radio frequency energy, the bomb is equipped with a small antenna IE5 as illustrated in Fig. 10. A receiver for controlling the flight of the bomb is illustrated in Fig. 11. Such a receiver includes a detector I21, an audio frequency amplifier I29 the output of which is serially connected through the four frequency responsive relays 8?, 89, 9i and 83 as illustrated in Fig. 8. These relays are utilized in the same manner to control the reversible motors I85 and IE9 and thereby the vanes 25 and 21.

A particular advantage of the system in accordance with this invention is that control of the bomb is efie-cted without the necessity of 0bserving the bomb during its flight. In addition, if the control is interrupted for a short period, as by an intervening cloud or smoke, the control apparatus automatically follows the calculated path of the bomb so that control may be reestablished as soon as the beam again reaches the falling bomb. In fact, it may be desirable to establish control only after the bomb has fallen for a considerable distance. At such a time, the angle bebeam of radio frequency tween the path of the bomb and the control beam is minimized so that the bomb is following a path more nearly parallel to the axis of the beam. In such a case, a more accurate control is established and slight errors in the cam mechanism tending to point the beam in a slightly incorrect direction at any given instant are not so apt to focus the beam entirely away from the bomb. Furthermore, although it is desirable to maintain the airplane in a straight path after releasing the bomb, at great altitudes slight variations in its position do not seriously affect the angle of the beam so that control is not lost nor is the beam moved so far as to deflect the bomb too far from its normal trajectory. The radio control system I is, of course, unaffected by intervening clouds, although it will be appreciated that the efiiciency of the bomb sight itself may be somewhat affected. Since the present invention is a corrector or Vernier for present bombing methods, it follows that the result can be no worse than those achieved by present methods even if, through some unforeseen circumstance, control is never established on the bomb. On the other hand, the system can operate to control the. flight of the bomb to greatly increase the accuracy and to produce a larger number of direct hits.

I claim as my invention:

1. In a system for directing an object falling from an airplane to a target on the ground, the combination including beam-producing means for radiating downwardly from said airplane a beam of radiant energy, sighting means angularly adjustable with respect to said radiating means for establishing a line and said target, means connected to said sighting means and said beam-producing means and initiated with the release of said object for automatie cally decreasing the angle between said beam and said line of sight as a function of the time required for said object to fall to ground so that said beam continuously intersects the calculated instantaneous position of said object as it falls toward said target, and receiving means on said object responsive to said object within said beam whereby said object is automaticall directed to said target.

2. In a system for directing an object falling from an airplane to a target on the ground, the combination including beam-producing means for radiating downwardly from said airplane a beam of light, sighting means angularly adjustable with respect to said radiating means for establishing a line of sight between said airplane and said target, means connected to said sighting means and said beam-producing means and initiated with the release of said object for automatically decreasing the angle between said beam and said line of sight as a function of the time required for said object to fall to ground so that said beam continuously intersects the calculated instantaneous position of said object as it falls toward said target, and receiving means on said object responsive to said beam for maintaining said object within said beam whereby said object is automatically directed to said target. 7

3. In a system for directing an objectfalling from an airplane to a target on the ground, the combination including beam-producing means for radiating downwardly from said airplane a energy, sighting means angularly adjustable with respect to said radiating means for establishing a line of sight between said airplane and said target, means connected to saidsighting means and said beam-proof sight between said airplane said beam for maintaining said object for automatically decreasing the angle between said beam and said line of sight as a function of the time required for said object to .fall to ground so that said beam continuously intersects the calculated instantaneous position of said object as it falls toward said target, and receiving means on said object responsive to said beam for maintaining said object Within said beam whereby said object is automatically directed to said target.

4. In a system for directing an object falling from an airplane to a target on the ground, the combination including beam-producing means for radiating downwardly from said airplane a beam of radiant energy, sighting means for establishing a line of sight between said airplane and said target, said sighting means being adjustably mounted in said airplane so that an observer may maintain a sight on said target, means for establishing an initial angle between said beam and said line of Sight, means initiated with the release of said object for automatically decreasing the angle between said beam and said line of sight as a function of the time required for'said object to fall to ground so that said beam continuously intersects the calculated instantaneous position of said object as it falls toward said target, and receiving means on said object responsive to said beam for maintaining said object within said beam whereby said object is automatically directed to said target. I

5. In a system for directing an object falling from an airplane to a target on the ground, the combination including beam-producing means for radiating downwardly from said airplane a beam of radiant energy, 7 a line of sight between said airplane and said target, means for establishing an initial angle between said beam and said line of sight, means initiated with the release of said object for automatically decreasing the angle between said beam and said line of sight so that said beam continuously intersects the calculated instantaneous position of said object as it falls toward said target,

receiving means on said object responsive to said beam for maintaining said object within said beam whereby said object is automatically directed to said target.

6. In a system for directing an object falling from an airplane to a target on the ground, the combination including beam-producing means for radiating downwardly from said airplane a beam of radiant energy, means for differently characterizing difierent portions of said beam, means for establishing a line of sight between said airplane and said target, means for establishing an initial angle between said beam and said line of sight, means initiated with the release of said object for automatically decreasing the angle be,- tween said beam and said line of sight so that said beam continuously intersects the calculated instantaneous position of said object as it falls toward said target, receiving means on said object responsive to said beam, an output circuit for said receiving means including control means operable in response to the reception .of energy characterized according to saiddifferent portions of said beam, respectively, and steering means for said object under control of said control means for maintaining said object within said beam.

7. In a system for directing'an object falling from an airplane to a target on the ground, the combination including beam-producing means for radiating'downwardiy from said airplane a sighting means for establishing 9, beam of radiant energy, modulating means for differently characterizing different portions of said beam, sighting means for establishing a line of sight between said airplane and said target, said sighting means being adjustably mounted in said airplane so that an observer may maintain a sight on said target, means for establishing an initial angle between said beam and said line of sight, said means comprising a cam-controlled link mechanism interconnecting said sighting means and said beam-producing means, means initiated wtih the release of said object for antomatically decreasing the angle between said beam and said line of sight so that said beam continuously intersects the calculated instantaneous position of said object as it falls toward said target, receiving means on said object responsive to said beam, an output circuit for said receiving means including control means operable in response to the reception of energy characterized according to said diiTerent portions of said beam, respectively, and steering means for said object under control of said control means for maintaining said object within said beam.

8. In a system for directing an object falling from an airplane to a target on the ground, the combination including beam-producing means for radiating downwardly from said airplane a beam of radiant energy, sighting means for establishing a line of sight between said airplane and said target, means for establishing an initial angle between said beam and said line of sight, means initiated with the release of said object for antomatically decreasing the angle between said beam and said line of sight so that said beam continuously intersects the calculated instantaneous position on said object as it falls toward said target, said means comprising a cam-controlled link mechanism interconnecting said sighting means and said beam-producing means, and receiving means on said object responsive to said beam for maintaining said object within said beam whereby said object is automatically directed to said target.

9. In a system for directing an object falling from an airplane to a target on the ground, the combination including beam-producing means for radiating downwardly from said airplane a beam of radiant energy, sighting means for establishing a line of sight between said airplane and said target, said sighting means being adjustably mounted in said airplane so that an observer may maintain a sight on said target, means for establishin an initial angle between the axis of said beam and said line of sight, means comprising a cam-controlled link mechanism interconnecting said sighting means and said beam-producing means, whose operation is initiated with the release of said object for automatically decreasing the angle between said beam and said line of sight as a function of the instantaneous relative positions of said object, said airplane and said target, so that said beam continuously intersects the calculated instantaneous position of said object as it falls toward said target, said angle reaching zero in a period of time equal to the time required for said object to fall to ground, receiving means on said object responsive to said radiant energy for modifying the normal trajectory of said object so as to maintain said object within said beam, whereby said object is automatically directed to said target.

10. In a system for directing an object falling from an airplane to a target on the ground, the combination including beam-producing means for radiating downwardly from said airplane a beam of radiant ener y, means for difierently characterizing different portions of said beam, means for establishing a line of sight between said airplane and said target, said sighting means being adjustably mounted in said airplane so that an observer may maintain a sight on said target, means for establishing an initial angle between said beam and said line of sight, means including a cam-controlled link mechanism interconnecting said sighting means and said beam-producing means for automatically decreasing the angl between said beam and said line of sight upon the release of said object as a function of the time required for said object to fall to ground so that said beam continuously intersects the calculated instantaneous position of said object as it falls toward said target, said angle reaching zero in a period of time equal to the time required for said object to fall to ground, receiving means on said object responsive to said beam, an output circuit for said receiving means including control means operable in response to the reception of energy characterized according to said different portions of said beam, respectively, and steering means for said. object under control of said control means for maintaining said object within said beam whereby said object is automatically directed to said target,

11. In a system for directing an object falling from an airplane to a target on the ground, the combination including beam-producing means for radiating downwardly from said airplane a beam of radiant energy, modulating means for differently characterizing said beam in four quadrants, each quadrant being modulated at a difierent frequency, sighting means for establishing a line of sight between said airplane and said target, means connected to said sighting means and said beam-producing means and initiated with the release of said object for automatically decreasing the anglebetween said beam and said line of sight as a function of the time required for said object to fall to ground so that said beam continuously intersects the calculated instantaneous position of said object as it falls toward said target, receiving mean on said object responsive to said beam, and an output circuit for said receiving means including frequency responsive relays operable to control the trajectory of said object in response to the reception of energy characterized according to the modulation of said quadrants, whereby said object is automatically directed to said target.

12. The method of controlling the trajectory of an object falling from an aircraft to a target on the ground including the steps of generating a beam of radiant energy, directing said beam downwardly from said aircraft, establishing and maintaining a line of sight between said aircraft and said target, varying the angle between said beam and said line of sight throughout a period coinciding with the time required for said object to fall from said aircraft to said target, receiving said radiant energy at said object, and utilizing said received energy to maintain said object in said beam so that said object is directed (/0 said target.

13. The method of controlling the trajectory of an object falling from an aircraft to a target on the ground including the step of generating a beam of radiant energy, directing said beam downwardly from said aircraft, establishing and maintaining a line of sight between said aircraft and said target, establishing an initial angle between said beam' and said line of sight, varying the angle between said beam' and said line of sight throughout a period coinciding with the time required" for said object to fall from said aircraft to said target, receiving said ta diant energy at said object, and utilizing'said received energy to maintain said object insaid beam so that said object is directed to said target.

14. The method of controlling the trajectory of 'an'object falling from an aircraft to atarget on the ground including the steps of'generating a beam of radiant energy,'directing said beam,

downwardly from said aircraft, modulating said beam, establishing and maintaining a line of sight between said aircraft and said target, varying the angle between said beam and said line of sight throughout a period coinciding with the time required for said object to fall from said aircraft to said target, receiving said radiant energy at said object, demodulating said received energlh'and utilizing said demodulated energy to vary the trajectory of said object to thereb maintain said object in said beam.

r '15. The method of controlling the trajectory of an object falling from an aircraft to a target on the groundincluding the steps of generating a beam of radiant energy of generally circular rents to control the trajectory of said object cross-section, directing said beam downwardly from said aircraft, difierentially characterizing difierent quadrants of said beam in accordance with different modulating voltages, receivingsaid radiant energy at said object, demodulating said received energy, separating currents characterized according to the respective modulation frequency of the quadrant of said beam impinging on said object, and utilizing said separated ourand maintain it Within'said beam.

16. The method of controlling the trajectory of an object falling from an aircraft to a target on the ground including the steps of generating a beam of radiant energy, establishing and maintaining a line of sight between said aircraft and said target, establishing an initial angle between the axis of said beam and said line of sight, varying said angle between said initial value and zero in a period coinciding with the falling of said object, controlling said variation so that said beam continuously intersects the calculated instantaneous position of said object, said beam and said line of sight reaching parallelism at the conclusion of said period, receiving said radiant energy at said object, and utilizing said received energy to maintain said object in said beam so that said object is directed to said target.

ALDA v. BEDFORD. 

